It is well known to package integrated circuits (dies) by placing them on a die-pad area of a lead frame with their electric contacts facing away from the lead frame. Wire bonds are formed between electric contacts of the die and lead fingers of the frame, a resin body is moulded around the integrated circuit and wires, and then the dam-bars are cut to separate each lead finger before singulation. This produces a “leaded” package, that is one having leads protruding from the sides.
An alternative to leaded packages where the lead frame is the carrier is the TAPP (thin array plastic package) packaging method, in which the integrated circuit is wire bonded to an array of electrical contacts supported on the surface of a laminar element. An integrated circuit it put onto the laminar element, and its electrical contacts are wire bonded to the respective electrical contacts supported by the substrate. Then the integrated circuit and wire bonds are encapsulated in an encapsulant, and the laminar element is removed by etching.
Another alternative to leaded packages where the lead frame is the carrier are BGA (ball grid array) packages. In one known BGA technique, the integrated circuit is mounted on the upper face of a laminar substrate, with the contacts of the integrated circuit facing away from the substrate. Wire bonds are formed to connect the electric contacts on the integrated circuit to contact points on the substrate. The electric contact points on the substrate are laterally spaced from the integrated circuit (i.e. to the sides of the integrated circuit), and in contact with respective electric paths which lead through the substrate to bumps on the substrate's lower surface. The substrate includes internal electrical paths parallel to the plane of the integrated circuit, so that the pattern of bumps is not the same as the pattern of the electric contact points on the substrate. The integrated circuit is then encased in plastic resin.
Another known leadless technique is known as the BCC (bump chip carrier) technique. In this case, an integrated circuit is placed onto a surface with its electric contacts facing upward. Areas of the surface to the sides of the integrated circuits include multiple depressions and a layer of conductive material is deposited over the surface. Wire bonding is used to directly connect contacts on an upper side of an integrated circuit to the portions of conductive material in the depressions. Resin is applied to encase the integrated circuit and the wires, and then the substrate is removed. Portions of the conductive layer between the depressions are selectively removed by an etching technique, so that the lower surface of the package is composed of the resin layer and protruding from it electrically conductive bumps which are the remains of the conductive material in the depressions. The bumps are laterally spaced from the footprint of the integrated circuit, i.e. there are no bumps directly beneath the integrated circuit.
There is continuing pressure to increase the number of inputs and outputs of the integrated circuit without increasing its size. One technique which has been proposed to achieve this is to mount a first integrated circuit on a lead frame, and a second integrated circuit onto the first. Both the integrated circuits are connected by wire bonds to the leadframe.
A further known packaging technique employs a integrated circuit called a flip chip. The flip chip carries electric contacts on one of its major surfaces, and this surface is placed attached face-to-face with a surface of a substrate having an organic laminate or inorganic laminate structure. The electric contacts of the flip chip are connected by solder bumps to circuitry which extends through the structure.